1. Field of the Invention
The present invention relates to a double wrap brake band apparatus used in an automatic transmission.
2. Related Background Art
A conventional double wrap brake band apparatus generally used in an automatic transmission will firstly be described. FIG. 9 is a front view showing a condition that a substantially C-shaped double wrap brake band apparatus 510 is disposed around an outer periphery of an inner race (drum) 528.
The double wrap brake band apparatus 510 comprises an intermediate band 512 and outer bands 514, 516. A connection member 536 is secured to one circumferential ends of the outer bands 514, 516 by rivets, and an anchor bracket 531 having a hole 530 for receiving an anchor pin 532 is secured to the other circumferential ends (free ends) of the outer bands 514, 516 by rivets.
On the other hand, the intermediate band 512 has one end (free end) received circumferentially between the outer bands 514, 516 and the other end spaced apart from the one end in a circumferential direction and secured to the connection member 536 by rivets in a condition that the other end is protruded circumferentially between the outer bands 514, 516.
Further, the intermediate band 512 is provided at its outer peripheral surface with an apply bracket 526 having a receiving surface 546a for receiving an urging force from an urging piston.
The double wrap brake band apparatus 510 having the above-mentioned construction is secured via the anchor pin 532 secured to the anchor bracket 531 and receives torque when the brake band apparatus tightens the inner race 528 by urging (downwardly in FIG. 9) the apply bracket 526 by means of an urging piston 520 having a base portion 522 and an urging rod 524.
FIG. 10 is a side view of the arrangement shown in FIG. 9. Friction materials 534 are adhered to inner peripheral surfaces of the intermediate band 512 and the outer bands 514, 516. As shown, from a released condition of the inner race 528, when the urging piston 520 is protruded or extended to urge an acting portion 546 of the apply bracket 526 downwardly, a force is transmitted to lower portions of the intermediate band 512 and the outer bands 514, 516. As a result, although the anchor bracket 531 tries to shift downwardly through the connection member 536, since the movement of the anchor bracket is prevented by the anchor pin 532, the intermediate band 512 and the outer bands 514, 516 tighten an outer peripheral surface of the inner race 528, thereby braking rotation of the inner race 528.
By the way, when the double wrap brake band apparatus 510 is used in the automatic transmission, a torque capacity to be allotted is varied with a using condition. For example, at a first speed in an R range or a D range, although high torque is allotted, torque to be allotted during transmitting may be about 1/10 of such high torque. However, in the transmitting, although the inner race 528 must be held for a very short time, since the double wrap brake band apparatus 510 has windings greater than a single winding brake band apparatus (not shown), the shifting amount of the urging piston 520 is increased accordingly, with the result that there arises a problem that it takes a relatively long time for completion of the operation of the double wrap brake band apparatus.